chapter 3

Question 1

how do computers communicate with each other?

Answer 1

by sending network messages

Question 2

how do programs send / receive network messages?

Answer 2

through sockets

Question 3

what is a socket?

Answer 3

is an endpoint in a 2 way communication link between 2 programs running on the same network

Question 4

what are communication paradigms built from?

Answer 4

sockets

Question 5

what are the 2 type of networks?

Answer 5

circuit switched and packet switched

Question 6

what is circuit switching?

Answer 6

is a network that relies on a physical connection b/n 2 nodes for communication

Question 7

what network guarantees constant QOS?

Answer 7

circuit switching

Question 8

what is packet switching?

Answer 8

is a network that splits a message into packets to transmit them independently over a digital network

Question 9

what is internet protocol?

Answer 9

a unique address that identifies a device on a network

Question 10

what do we mean when we say IP offers no guarantees?

Answer 10

packets may get:
- lost
- delivered twice
- corrupted
- delivered in wrong order

Question 11

what is UDP?

Answer 11

a transport protocol that does not guarantee the delivery or the ordered delivery of datagrams [ packets ]

Question 12

what is TPC?

Answer 12

a bidirectional transport protocol that provides reliable [ data ] packet flow b/n devices

Question 13

how are network addresses represented in UNIX?

Answer 13

a generic struct sockaddr.
- for internet we use sockaddr_in

Question 14

what is a domain name?

Answer 14

a human readable IP address

Question 15

what is DNS?

Answer 15

a domain name service translates human readable domain names to machine readable IP address

Question 16

how is domain name converted to IP?

Answer 16

using : gethostbyname ()

Question 17

list TCP based protocols?

Answer 17

• TELNET
• FTP
• HTTP
• SMTP
• SSH

Question 18

in sockets, what are the roles of:
- socket ()
- connect ()
- bind ()
- listen () and
- accept ()

Answer 18

1. creates socket
2. allows client to initiate a connection to server
3. specifies socket id
4. listen for a connection
5. blocks process til incoming connection is received

Question 19

what are socket function calls in TCP client side?

Answer 19

socket, connect , write , read, close

Question 20

what are socket function calls in TCP server side?

Answer 20

socket, bind, listen, accept, read, write, read, close

Question 21

how are TCP sockets created by default?

Answer 21

as client socket

Question 22

which type of socket can’t receive incoming connection?

Answer 22

client socket

Question 23

which type of socket allocates resources for connections?

Answer 23

server socket

Question 24

how can we convert a client socket to a server socket?

Answer 24

by using listen( ) and specifying how many connections can be supported in parallel

Question 25

what arguments does the listen() function call take and what does it return?

Answer 25

1. sockfd - socket discriptor 2. backlog - size of buffer [ limits no of pending connections, not accepted conn] returns: - 0 for success and -1 for error

Question 26

what arguments does the connect() function call take and what does it return?

Answer 26

1. sockfd - socket discriptor 2. serv_addr - where to connect [ sockaddr_in ] 3. addrlen - length of address returns - 0 for s -1 for f

Question 27

which socket function call binds client's address to a random unused port?

Answer 27

connect( )

Question 28

what does accept( ) function call do when once a conn is received?

Answer 28

- creates a dedicated socket for it - old socket goes back to waiting for other conns

Question 29

what arguments does the accept( ) function call take and what does it return?

Answer 29

1. sockfd 2. addr - address of client [ sockaddr_in ] 3. addrlen returns: - descriptor of new socket or -1

Question 30

what arguments does the write( ) function call take and what does it return?

Answer 30

1. sockfd 2. buff - buffer to be sent 3. count - buffer size returns: - no of bytes sent or -1

Question 31

what arguments does the read( ) function call take and what does it return?

Answer 31

1. sockfd 2. buff - buffer where to write the read data 3. count - buffer size returns: - no of bytes read or -1

Question 32

which socket function call blocks process until data is received from socket?

Answer 32

read( )

Question 33

for what reason could a write( ) call send less bytes than requested?

Answer 33

- due to limitations of kernel buffer, so always check return bytes and resend unsent data

Question 34

when does read( ) return 0?

Answer 34

when notifying end of file EOF

Question 35

what socket function calls block process when executing?

Answer 35

read and accept

Question 36

what is multiplexing?

Answer 36

is a way of sending multiple signals or streams of information through a socket [ communication link ]

Question 37

what are the methods to achieve multiplexing?

Answer 37

1. using multiple processes 2. using non blocking I/O 3. using select( ) 4. using poll( )

Question 38

how does using multiple processes to achieve multiplexing work?

Answer 38

poorly, consumes resources and is hard to program

Question 39

how does using non-blocking I/O to achieve multiplexing work?

Answer 39

works for read( ) but not accept( )

Question 40

how does using select( ) monitor to achieve multiplexing work?

Answer 40

blocks the program until something [ read / write ] happens on the socket

Question 41

how does using poll( ) to achieve multiplexing work?

Answer 41

similarly to select( ), but provides additional info about streams

Question 42

list structures of a server?

Answer 42

- iterative - 1 child / client - pre-forked - select loop

Question 43

briefly explain iterative server structure.

Answer 43

- 1 req after another - long queue [ accept( ) ] - higher latency - low resource utilization

Question 44

briefly explain 1 child / client server structure.

Answer 44

- new process created for every conn - concurrent handling of requests - not suitable for highly loaded servers

Question 45

which server structure is the most common among concurrent servers?

Answer 45

1 child / client

Question 46

briefly explain per-forked server structure.

Answer 46

- server creates pool of processes - good for highly loaded servers - allows limitation on num of processes created

Question 47

how does the pre-forked server variant work?

Answer 47

with thread pools instead of process pools

Question 48

what is the downside of pre-forked servers?

Answer 48

- accept( ) requires the use of synchronization lockmutex( ) -> accept( ) -> unlockmutext( )

Question 49

briefly explain select loop server structure.

Answer 49

- difficult to do correctly - read more man idk